24 THE MICROSCOPIC PREPARATION. 



Osmic acid is a reagent that kills quickly, fixes protoplasm exceed- 

 ingly well, but nuclei not so well, and colors certain tissues. Only 

 small pieces can be fixed in this fluid, as it does not easily penetrate the 

 tissues. It is ordinarily used in a \ c / f to \ c / (l aqueous solution, the 

 objects remaining immersed twenty-four hours. They are then washed 

 in running water for the same length of time, after which they are trans- 

 ferred to 90 ^r alcohol. Very small objects may be treated with osmic 

 acid in the form of vapor (vaporization). This is done as follows: A 

 very small quantity of osmic acid solution is put in a small dish. The 

 object is then suspended by a thread in such a way that it does not come 

 in contact with the fluid. The dish should be covered with a well-fitting 

 lid. 



Flemming's Solution. A solution with a similar action, but fixing 

 nuclear structures better than osmic acid, is the chromic-osmic -acetic 

 acid solution of Flemming : 



Osmic acid, I c /c aqueous solution . . . . lo parts. 

 Chromic acid, \ c /o aqueous solution ... 25 " 

 Glacial acetic acid, \ r /o aqueous solution . 10 " 

 Distilled water 55 " 



Small pieces are fixed in a small quantity of the fluid for at least 

 twenty-four hours, sometimes for a longer period, extending even to 

 weeks. They are then washed for twenty-four hours in running water and 

 passed through 50%, 70%, and 80%, each twenty-four hours, into 90% 

 alcohol. 



Flemming also recommends a stronger solution, which is made as 

 follows : 



O^mic acid, 2^ aqueous solution .... 4 parts. 

 Chromic acid, \ c /c aqueous solution ... 15 " 

 Glacial acetic acid I part. 



FoPs Solution. Fol has recommended the following modification 

 of Flemming's solution : 



Osmic acid, I c /o aqueous solution .... 2 parts. 

 Chromic acid, i ( / c aqueous solution ... 25 " 

 Glacial acetic acid, 2 f / c aqueous solution .5 " 

 Distilled water 68 " 



The after-treatment is the same as for Flemming's solution. 



Hermann's Solution. Very good results sometimes follow the 

 use of the platinum-acetic-osmic acid solution of Hermann (89, i). It 

 is employed as is Flemming's solution : 



Osmic acid, 2% aqueous solution .... 4 parts. 

 Platinum chlorid, I % aqueous solution . . 15 " 

 Glacial acetic acid I part. 



After fixing with this solution, Flemming's solution, or any other 

 osmic mixture, the subsequent treatment with alcohol may be followed 

 by crude pyroligneous acid. The objects are placed for from twelve to 

 twenty-four hours in the latter and then again immersed in alcohol. The 

 result is a peculiar coloring of the specimen which often makes subsequent 

 staining (see below) unnecessary (Hermann). 



Corrosive Sublimate An excellent fixing fluid is made by 

 saturating distilled water or a physiologic saline solution (see p. 22) with 



